A multiplicity of power stations have been built throughout the world over the past decade that are based on a combined gas/steam turbine process and by means of which the noxious discharge can be significantly reduced. Said stations are referred to as combined gas and steam power stations.
In the case of a sub-type of combined gas and steam power stations—what are termed IGCC power stations (“IGCC” being an acronym of “Integrated Gasification Combined Cycle”)—the combined gas and steam power station additionally has an integrated fuel gasification unit by means of which a liquid fuel—for example oil—or a solid fuel—for example a mineral—, brown coal, or biomass—is converted in a gasifier into a synthesis gas which is then combusted in a gas turbine. The synthesis gas is as a rule cleaned before being combusted. Viewed overall, noxious substances are in that way separated off even before combustion takes place, or are not produced at all.
Oxygen is required for gasifying the fuels to produce synthesis gas. For producing the oxygen, IGCC power stations have air separation units in which, besides the necessary oxygen, mainly nitrogen is produced from the ambient air through fractional distillation. The synthesis gas has to be cooled prior to further treatment. During the cooling process steam is produced which, among other things, contributes to generating current in the steam turbine of the IGCC power station. Filters first keep back ash particles when the gas has been cooled, then carbon dioxide can also be removed if required. Other noxious substances such as sulfur compounds and heavy metals are bound likewise by means of chemical and physical processes. The necessary fuel purity for operating the gas turbines and low emissions from the IGCC power station are realized thereby.
Upstream of the combustion chamber of the gas turbine the synthesis gas is if necessary mixed with nitrogen from the air separation unit and/or with water vapor in order to condition the fuel-gas mixture in accordance with the gas turbine's requirements. The working gas then produced from combusting with air is expanded in the turbine stages of the gas turbine.
The exhaust gas is released to the atmosphere once the working gas has been expanded in the gas turbine and the waste heat has then been utilized in a steam generator.
The streams of steam from the crude- and waste-gas cooling process are combined and jointly fed to the steam turbine. After being expanded in the steam turbine, the steam is condensed via a condenser and the condensate fed back via the feed-water container into the water cycle or, as the case may be, steam cycle.
An IGCC plant of said type is known from, for example, WO 03/008768. Said plant has a gasification device in which particulate coal is combusted together with oxygen and steam to produce a synthesis gas (partial oxidation). After several processing steps the synthesis gas is fed as a gaseous fuel to a gas turbine combustion chamber.